The interferon system is a current prime area of investigation in our laboratory. During the coming year we shall pursue the following studies: 1. The capacity of cell hybrids to produce human interferon depends on genetic elements in chromosomes 2 and 5. Various possible explanations for dual genetic factors are: (a) subunit interacting elements, (b) receptor function for interferon inducers plus structural gene for interferons, and (c) genetic element which codes for processing enzyme plus the structural gene for interferon. We shall attempt to identify the responsible mechanism. 2. The mechanism for the AVP locus is unknown. Possibilities range from a receptor protein for interferon to a specific amino acyl t-RNA synthetase which is regulated by interferon. We shall begin to test these possibilities. 3. We now possess a parasexualsystem for studying interferon genetic control in the mouse. These studies will be pursued.